Technological development and increased demand for mobile equipment have led to a rapid increase in the demand for secondary batteries as an energy source. Among these secondary batteries, a great deal of research and study has been focused on lithium secondary batteries having a high-energy density and a high-discharge voltage and consequently some of such lithium secondary batteries are commercially available and widely used.
The lithium secondary battery refers to a battery comprising an electrode assembly composed of a cathode containing a cathode active material capable of undergoing intercalation/deintercalation of lithium ions, an anode containing an anode active material capable of undergoing intercalation/deintercalation of lithium ions, and a microporous separator disposed between the cathode and anode, in conjunction with a lithium ion-containing non-aqueous electrolyte.
For example, as the cathode active material for the lithium secondary battery, mention may be made of primarily transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNiO2), or composite oxides wherein a portion of such a transition metal in the oxide is substituted with other transition metals. In addition, as the anode active material, amorphous carbon-based materials and crystalline carbon-based materials are largely used with recently active investigation on utilization of silicon-based materials as the anode active material.
Such a secondary battery is broadly divided into a jelly-roll (winding) type and an overlap (stacking) type, depending upon a construction form of the electrode assembly composed of cathode/separator/anode. The jelly-roll type electrode assembly is fabricated by coating an electrode active material on metal foil as a current collector, pressing and cutting the resulting structure into a band form having a desired width and length, and isolating the cathode and the anode using a separator, followed by spiral winding. The jelly-roll type electrode assembly is suitable for cylindrical batteries, but suffers from various problems such as separation of the electrode active materials from electrodes and poor spatial utilization and efficiency, upon application thereof to a prismatic or pouch-type battery.
The more advanced stacked-type electrode assembly, which is capable of solving the aforementioned disadvantages and problems, as detailed in Korean Patent Application Publication Nos. 2001-82058 A1, 2001-82059 A1 and 2001-82060 A1, assigned to the present applicant, is configured to have a structure in which full cells of cathode/separator/anode having a given size or bicells of cathode(anode)/separator/anode(cathode)/separator/cathode(anode) having a given size are sequentially stacked such that the cathode and the anode are arranged opposite to each other with a separator therebetween.
Generally, the secondary battery is fabricated by putting the electrode assemblies, having various configurations as described above, into a cylindrical or prismatic metal can or a pouch-type sheet case, and sealing the resulting structure with exposure of an electrode terminal pair of the cathode and anode to the outside of the battery case. Therefore, one battery cell is configured to supply only a specific voltage within a given range. Some of conventional prior arts provide a structure having formation of two or more electrode terminals on the outside of the battery case so as to enhance power output efficiency, but the voltage provided from the overall battery cell is still constant.
Whereas, as electric/electronic devices are developed into highly various forms, there may also be necessary devices having a configuration requiring one or more operation voltages depending upon desired operation modes. For implementation of such a device requiring two or more operation voltages, a currently available technique is only a method involving a combined use of two or more secondary batteries having different operation voltages set to each other.
As an attempt to provide two operation voltages from one battery, Japanese Unexamined Patent Publication No. 2003-331813 discloses a battery having two battery cells (A, B) within one battery case in an isolated state from one another, wherein electrode terminals for each battery cell (A, B) are exposed to the outside. The aforesaid Japanese Patent is characterized in that the battery is configured, for example, by divisional arrangement of a 1.5 V-power battery cell (A) and another 1.5 V-power battery cell (B) within one battery case, and connection of a cathode terminal and an anode terminal to each of the battery cells (A, B), such that a desired voltage can be achieved using the aforementioned single battery without a need for a series connection of two 1.5 V batteries, upon use of the battery in the device operating at 3.0 V.
However, the battery of the above-mentioned Japanese Patent has an effect of using no members necessary for construction of a battery module, such as a spacer, by simple installation of two battery cells inside the battery case, but provides substantially no different voltages between two battery cells. Based on the disclosure of the above Japanese Patent, there may be considered to configure the battery such that the battery cell (A) and the battery cell (B′) provide different voltages therebetween. For this purpose, there are, however, fundamental problems such as a need for a separate structure for divisional arrangement of the battery cells (A, B′) inside the battery case.
Consequently, there is a need for the development of a technology that is capable of providing a plurality of voltages from one battery without a significant modification of the structure in a conventional secondary battery.